Which of the following is NOT a valid feature of IPv6 compared to IPv4?

IPv6 does not replace TCP and UDP protocols with SCTP. Instead, TCP and UDP remain as the primary transport-layer protocols for IPv6, ensuring backward compatibility with existing applications. SCTP is an additional transport protocol introduced to handle new use cases like multimedia streaming, but it is not mandatory in IPv6. This design decision was intentional to maintain compatibility and provide flexibility. For instance, applications developed for IPv4 networks using TCP/UDP do not need significant changes to operate in an IPv6 environment. IPv6 focuses on expanding address space, enhancing routing efficiency, and improving security while retaining compatibility with existing transport-layer protocols. Why Other Options Are Incorrect :

1. IPv6 uses 128-bit addressing : Correct. IPv6 expands the address space exponentially compared to IPv4, solving address exhaustion issues.
2. IPv6 eliminates the need for NAT : Correct. With 128-bit addresses, IPv6 provides a unique address for every device, removing NAT's necessity.
3. IPv6 introduces multicast addressing but removes broadcast functionality : Correct. IPv6 replaces broadcasting with more efficient multicast and anycast methods.
4. IPv6 includes an in-built Quality of Service (QoS) mechanism in the header : Correct. The IPv6 header includes a Flow Label field to support QoS, unlike IPv4.